This project aims to learn more about a factor, in the blood of some sick human patients, that binds some peptides related to angiotensin. The factor was discovered accidentally in the course of measuring angiot@nsin in blood. It is a macromolecule that circulates free with a molecular weight of about 150,000, or bound to IgA-like protein with a total molecular weight of about 260,000. It is found in 1 to 2 percent of normal humans, 6 percent of hospitalized non-retarded patients, and 32 percent of hospitalized retarded humans. The goals of the project supported by this grant are to characterize the binder more completely, and find its origin and the significance of its appearance in the blood of retarded and other sick patients. A subordinate goal is the exploration of the use of this factor in measuring angiotensin congeners, since it is highly specific for those peptides with arginine at the amino-terminus, such as (des-asp1)-angiotensin II. BIBLIOGRAPHIC REFERENCES: Goodfriend, T.L., Sindel, M., Fyhrquist, F., Hong, R., Azen, E., and Stewart, J.M.: Peptide-binding macromolecules in the blood of seriously ill or mentally retarded patients. J. Lab. Clin. Med. 87: 299-319, 1976.